Rails isn't running destroy callbacks for has_many through join model -

i have 2 ar models , third has_many :through join model this:

class user < activerecord::base   has_many :ratings   has_many :movies, through: :ratings end  class movie < activerecord::base   has_many :ratings   has_many :users, through: :ratings end  class rating < activerecord::base   belongs_to :user   belongs_to :movie    after_destroy     puts 'destroyed'   end     end 

occasionally, user want drop movie directly (without directly destroying rating). however, when do:

# puts user.movie_ids # => [1,2,3]  user.movie_ids = [1, 2] 

the rating's after_destroy callback isn't called, although join record deleted appropriately. if modify user model this:

class user < activerecord::base   has_many :ratings   has_many :movies,      through: :ratings,     before_remove: proc { |u, m| rating.where(movie: m, user: u).destroy_all } end 

everything works fine, ugly, , rails tries delete join model second time.

how can use dependent: :destroy strategy association, rather dependent: :delete?

answering own question, since difficult google, , answer super counter-intuitive (although don't know ideal interface be).

first, situation described thoroughly here: https://github.com/rails/rails/issues/7618. however, specific answer buried halfway down page, , issue closed (even though still issue in current rails versions).

you can specify dependent: :destroy these types of join model destructions, adding option has_many :through command, this:

class user < activerecord::base   has_many :ratings   has_many :movies,      through: :ratings,     dependent: :destroy end 

this counter-intuitive because in normal cases, dependent: :destroy destroy specific association's object(s).

for example, if had has_many :ratings, dependent: :destroy here, of user's ratings destroyed when user destroyed.

we don't want destroy specific movie objects here, because may in use other users/ratings. however, rails magically knows want destroy join record, not association record, in case.